Frankly the problem is that the D&D stats are not pinned down to a specific quality.
Strength is not just your fast action muscles, nor your bulk, nor anything like that - it's a combination of many factors. It's up to the player to decide how his character's strength manifests.
Constitution is not just a characters tolerance for pain - it also covers his resistance to drugs, some magic etc etc. Again - up to the player to represent.
Dexterity: spryness, quickness, manual accuracy etc. Up to the player.
Wisdom, intelligence - same thing. Up to the player. So mixed up you can't really seperate out exactly what each attribute covers except in game terms.
Charisma. Same again - how nice the guy looks, how big his smile is, how he speaks, the force of his personality. All this falls under charisma. It's up to the player how he plays this - perhaps the high charisma paladin is simply grizzled, war-torn, gruff and very authoritative. Perhaps he's drop-dead gorgeous and has all the right moves.
There's no need to add an extra stat in. The current ones cover it nicely, and the player can add flavour to taste.
And all that's ignoring the effects of the disguise skill, the hat of disguise, alter self, polymorph self etc etc. All of which would blow a 'comeliness' stat out the window.
In short - too difficult to implement, and of limited to zero value in a game.